CS4723Software
Validation and Quality Assurance
Lecture 13Code Review
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Coding style Why?
Easier to read: for others and yourself
Less mistakes and misunderstandings
Reduce the requirement for comments and documentation (self-documented)
What? Coding style is not a very well organized topic
A lot of scattered and conflicting tips given by experienced developers
We organize all these tips from the smallest to the largest code elements (Identifier to File)
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Coding style and programming languages Coding style is mostly general
E.g., should not use too simple variable names
Coding style can be specific to programming languages in some cases Case sensitive / insensitive languages
Case sensitive: C family (including Java, python) Case insensitive: Basic, Fortran, Pascal, Ada Semantics for cases: Prolog (cap for var, low for names)
Indentation based compilation Python, Haskell
Different code structures Classes in OO languages, recursions in functional
languages
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Coding style: An exampleint f(String str, int val1, int val2){ //calculate str1 and str2 based on the formula string str1 = str.subString(str.indexOf(str.charAt(2*val1+10-val1)), str.lastIndexOf(String.charAt(val1)) - str.lastIndexOf(String.charAt(0))); string str2 = str.subString(str.indexOf(str.charAt(2*val2+10-val2)), str.lastIndexOf(String.charAt(val2)) - str.lastIndexOf(String.charAt(0)));
String resultforprint = str1 + str2; //concatenate str1 and str2 UI.initialize(); //initialized UI UI.sendMessage("Header"); //Send message "Header" to UI UI.sendMessage(resultforprint); int diff; …
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Coding style: An example … //if val1 larger than 10 and the diff of val2 and val1 is not 5, //or val2 is larger than 100, send the diff if(val1>10&&diff=(val2-val1)!=5||val2<100) UI.sendMessage("The diff is "+ diff); UI.sendMessage("Footer"); while(!this.comingMessage) UI.sendMessage("Waiting for next message"); this.count = this.count + 1; if(UI.success) return 0; //return 0 if UI.success is true return 1;}
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Variables and Constants Variable (function, method) Naming
Do not use names with no meanings (e.g., a, b, ac, xyz)
Do not use names with general meanings (e.g., do, run, it, value, temp)
Do not differentiate variables with simple number indexes (e.g., name_1, name_2, name_3)
Full words is better than abbreviations (e.g., use phone_number instead of tel)
Use underscore or Capitalized letter to separate words (e.g., phone_number or phoneNumber)
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Variables and Constants Hungarian Notations
Each variable has a prefix to indicate its type lAccountNum (long) arru8NumberList (array, unsigned 8 bit)
Quite useful in C, and is used widely in C++ and C#
MS code and Windows APIs use Hungarian Notations a lot
Not very necessary in OO languages with modern IDEs, because the type of a variable is complex in itself, and easy to know
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Variables and Constants Constants
Give a name to constants People know what it is Consistent modification
If global, collect all constants somewhere (e.g, Config class, or a configuration file)
Conventionally, the name for a class/file-wide constant is all Capitalized words, concatenated by underscore (e.g., MAX_DAY_LIMIT), be careful of case-insensitive languages
Don’t use ‘l’ for long integer, use ‘L’ instead Consider 10l, very confusing
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Variables and Constants String Constants
Try to avoid string constants in your code
Especially if they are related to UI (visible strings), system (paths), database (sql statements), or any environments
Put them in different configuration files according to their usage
So that you can change them later to generate different releases (different OS, regions, etc.)
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Expressions Avoid Complex expressions
Give names to intermediate results
Example: int totalAmount = (hasDiscount() && validForDiscount(user)) ?
discountRate() * getPrice() * getNum() : getPrice() * getNum();
-------------------------------------------------------------------
boolean validDiscount = hasDiscount() && validForDiscount(user);
int price = validDiscount ? getPrice() * discountRate() : getPrice();
int totalAmount = price * getNum();
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Expressions Avoid corner cases (uncommon operators)
Rules are complex, maybe changed (careful of updates!!)
e.g. i += j; always equals to i = i + j; ?
int a[] = {1, 5}; int i = 0; a[i] = i++; print (a[0]+”,” + a[1]);
What will be printed?
Add brackets even when you think it is unnecessary (except for + and * which is so well known)
Conditional Expressions Avoid abbreviation in some languages
e.g., use if (x!=0) instead of if (x)
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Statements/Lines One statement per line
Line breaks Set a maximum length for lines
Break lines at binary operators, commas, etc.
Put the binary operator at the beginning of the following line, why?
Indent the following sub-lines to differentiate with other code
e.g.,
if(long condition 1
&& long condition 2){
do something;
}
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Blocks Indentation
Do indentation for blocks (in method, loop, if-else conditions)
Pay more intention to indentation in Python and Haskell, it is a right or wrong thing!!
Try to avoid using tab, why? Tabs are translated to 2 or 4 spaces in different editors or
settings, resulting in global coding style problems, and the case is even worse for Python
2 (Lua, scala, ruby, …) or 4 spaces (others), usually depending on the language you use and the team convention you decided on
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Blocks Single statement blocks for loop and conditions
Add curly brackets around, why?
if(a > 1)
// do something; Error!!
another statement;
Logic blocks Divide a basic block to several logic blocks, add an
empty line between themint validDiscountRate = …;
int finalAmount = validDiscountRate * amount;
print getReceiptHeader();
print finalAmount;
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Blocks Code Clones
Copy and paste is a notorious programming habit
Simple but result in code clones
Inconsistent modification of different clone segments
Example: for (int i = 0; i < 4; i++){ sum1 += array1[i];}average1 = sum1/4; for (int i = 0; i < 4; i++){ sum2 += array2[i];}average2 = sum1/4;
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Blocks Code Clone Detection
Quite a number of tools: CCFinder, Deckard, Conqat, mostly for C, C++ and Java. VS.net 2013 also has the feature for C#
After Detection Eliminate (extract a method invoked by both places)
Sometimes not easy Want to reduce dependencies
Change other people’s code
20% code clones in industry / open source code
Try to keep track of them
VS.net may have a feature in near future
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Methods Size
Smaller, and smaller, and even smaller …
Usually less than 20 lines, and never exceed 100 lines
Why?
easier to understand
easier to reuse: less code clones
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Methods Signatures
Avoid too many parameters But still need dependency injection? How?
Group parameters to a new class
Example: Use some tools to compare old and new data, match
the diff to some pattern and output matching results doStatistics(String newDataPath, String oldDataPath,
String patternPath, String outputPath, String toolPath, …)
Generate a class called ConfigurationInfo doStatistics(ConfigurationInfo configInfo)
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Methods Contents
Try to not use global variables, especially writing global variables
Try to avoid unnecessary side effects
What are side effects?
Change the state of the object
Example: public getDepth(){ int depth = 0 while(!callStack.isEmpty()){ callStack.pop(); depth = depth + 1; } return depth;}
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Methods Relations
Try to avoid constraints between methods
Example:
public load(File f){ this.file = f; open(this.file);}public process(){ do things with this.file;}public clean(){ close(this.file)}
public load(File f){ this.file = f; open(this.file); this.content = readFrom(f); close(this.file)}public process(){ do things with this.content; open, write and close(this.file)}
Put everything in one method
or
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File Structure Follows the common structure of the language
(e.g., imports, class decl, fields, methods in Java, includes, macros, structs, functions in C)
Keep it small Usually no more than 500 lines
Should break a module to multiple sub-modules (it is also a design issue)
Put public methods before private methods Easier for other people to read public methods
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Coding style: An exampleint f(String str, int val1, int val2){ //calculate str1 and str2 based on the formula string str1 = str.subString(str.indexOf(str.charAt(2*val1+10-val1)), str.lastIndexOf(String.charAt(val1)) - str.lastIndexOf(String.charAt(0))); string str2 = str.subString(str.indexOf(str.charAt(2*val2+10-val2)), str.lastIndexOf(String.charAt(val2)) - str.lastIndexOf(String.charAt(0)));
String resultforprint = str1 + str2; //concatenate str1 and str2 UI.initialize(); //initialized UI UI.sendMessage("Header"); //Send message "Header" to UI UI.sendMessage(resultforprint); int diff; …
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Coding style: An example … //if val1 larger than 10 and the diff of val2 and val1 is not 5, //or val2 is larger than 100, send the diff if(val1>10&&diff=(val2-val1)!=5||val2<100) UI.sendMessage("The diff is "+ diff); UI.sendMessage("Footer"); while(!this.comingMessage) UI.sendMessage("Waiting for next message"); this.count = this.count + 1; if(UI.success) return 0; //return 0 if UI.success is true return 1;}
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Code convention for companies / organizations Most companies / organizations have their
code conventions Usually following the general rules of coding style
May set different line-length limits, 2 or 4 spaces, different ways to place braces, or whether to put spaces around operators or brackets, …
Some code convention examples:
http://www.oracle.com/technetwork/java/codeconv-138413.html Java conventions
http://msdn.microsoft.com/en-us/library/vstudio/ff926074.aspx
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Coding style enforcement: Eclipse Demo
Go to windows -> preferences -> Java (or other languages installed) -> coding styles -> formatter
Select an existing profile (e.g. eclipse built-in) or click on New… to generate a new one
Click on edit to open the edit panel Edit the profile: change brace rules, tab to space,
etc. Right click on your project -> preferences -> Java -
> coding styles -> formatter-> check project specific -> choose a formatter and click apply
To format existing code: Ctrl + Shift + F
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Comments A way to help other people and yourself to
better understand your code later
Common rules No need to comment everything
More important to explain variables than statements: Other developers know what the statement does, but do not know what the variable means…
Try to write complete sentences
Avoid code in comments, it make readers harder to read code
Clean commented code ASAP, you have version control, no need to preserve anything
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Comments for statements Two types of statements especially require
comments Declaration statements
Statements with complex expressions
How to write comments Example:
int score = 100; // set score to 100
TERRIBLE COMMENT!
int score = 100; // the full score of the final exam is 100
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Comments for Methods A well-structured format for each public
method
Explain: What the method does
What does the return value mean
What does the parameters represent
What are restrictions on parameters
What are the exceptions, and what input will result in exceptions
For private method, comment may be less structured, but still need to include the information
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Comments for Methods Example:
/** * Fetch a sub-array from an item array. The range * is specified by the index of the first item to * fetch, and ranges to the last item in the array. * * @param list represents the item list to fetch from * it should not be null. * @param start represents the start index of the * fetching range it should be between * 0 and the length of list * @return the fetched subarray */public List<Item> getRange(List<Item> list, int start){
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Comments for Classes/Files A well-structured comment for each class /
file
Include: Author (s)
Generating time and version
Version of the file
A description of the class/file about its main features, and usage specifications / examples
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Comments for Classes/Files Example:
/** * A mutable sequence of characters. The principal operations on a StringBuilder * are the append and insert methods. The append method always adds these * characters at the end of the builder; the insert method adds the characters at * a specified point. * * For example, if z refers to a string builder object whose current contents are * "start", then the method call z.append("le") would cause the string builder to * contain "startle", whereas z.insert(4, "le") would alter the string builder to * contain "starlet". * * author : John Smith * generate: Oct.1st.2013 * version : 1.0 * @since : 2.2 */public class StringBuilder{
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JavaDoc A JavaDoc Example
Ant 1.6.5
http://api.dpml.net/ant/1.6.5/overview-summary.html
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JavaDoc Structure
Overview
Packages
Classes / Interfaces / Exceptions
Fields / Constructors / Methods Hierarchy
Deprecated
Index
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JavaDoc-Tags Tags are meta-data put in the comments to
guide Javadoc in document generation
Starting with “@” @author : author of the class
@version: current version of the software
@since: the software version when the class is added
@see: a link to another class / method / …
@param: parameters of a method
@return: return value of a method
@exception: exceptions thrown from a method
@deprecated: an outdated method
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Javadoc: Mapping Commenting methods for documentation
/** * Constructs a WordTree node, specify its * data with the parameter word, both children * of the WordTree node are null * * @param word the string value stored as the data of the node, cannot be null * @exception NullWordException an exception raised when the parameter word is null */ public WordTree(String word) throws NullWordException{ ... /** * fetch the data of current WordTree node * @return the data stored at current node */ public String getData() ...
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Javadoc: Mapping Javadoc generated
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JavaDoc Demo for generating Javadoc in eclipse
Right click on your project Goto Export…, and choose Javadoc You will need a Java SDK (not only JRE) to run
Javadoc Set the Javadoc command to the Javadoc
executable Set the destination to the place Click on finish
